To prepare the sponge cake, combine egg whites and water in a mixing bowl. Using a standing mixer or hand mixer, whip egg whites, gradually sprinkling in sugar. Continue until soft peaks form.

Gradually fold in egg yolks into egg whites. Use a spatula to do this gently.

Combine baking powder and flour. Sift some flour into the egg mixture and gently fold flour in using a spatula. Repeat until all the flour is incorporated into egg mixture.

Butter and flour an 11-inch (28cm) Springform pan. Pour batter into pan and shake gently to make sure batter is distributed evenly. Bake for about 25 minutes or until a toothpick poked into center of cake comes out clean. Cake should have a nice golden brown (not dark brown) color. Allow cake to cool completely.

For the filling, whip Quark until smooth. Sift in some powdered sugar and whip until combined. Repeat until all the powdered sugar has been incorporated. Add vanilla sugar, salt, lemon zest, and lemon juice. Whip until combined.

In a small cooking pot, combine milk and gelatine. Heat until it just begins boiling, mixing often. Allow to cool to room temperature.

With the mixer going (with whip attachment), whip quark mixture while slowly drizzling in the gelatine. Continue to whip for another minute to make sure no lumps of gelatine develop.

In a separate bowl, whip the whipping cream. Add the "Whip It" and sugar and continue whipping until firm peaks form.

Gradually fold quark mixture into whipping cream. Use a spatula to do this gently. Continue folding until all quark has been incorporated into whipped cream. Mixer will be thick but slightly liquidy. This is okay because the gelatine will harden once chilled.

Slice the sponge cake into 2 even layers. Place the bottom half onto a cake plate. Spread a thin layer of fruit jam onto this layer of cake. On top of the jam, add one layer of fresh fruit.

Place the ring of the springform pan (simply remove the bottom of the springform pan) and place it around the cake & fruit layer. This will keep the filling in place. Make sure there are no spaces between the ring and the cake layer so that no filling leaks out. When this is in place, pour the filling over the fruit & cake layer. Smooth the top of the filling and place the top cake layer directly onto the top of the filling. Cover with plastic to prevent drying and refrigerate overnight for the filling to harden.